1. Field of the Invention
The present invention relates to an external storage device being connected to an information processing apparatus such as a personal computer (PC), and to an information processing apparatus, and in particular to an external storage device, such as a CD-ROM drive, having an audio function and being connected to an information processing apparatus, and to an information processing apparatus. More specifically, the present invention pertains to an external storage device that provides a power saving function for an information processing apparatus that is connected thereto, and that has an improved S/N (Signal/Noise) ratio at the audio mute time, and to an information processing apparatus.
2. Description of Prior Art
In accordance with recent technological developments, various types of personal computers (PCS), such as desktops, towers and notebooks, have been produced and are being sold. The notebook PCS are so designed to be compact and light, while taking into account the portability and mobile, outdoor use.
One of the features of a notebook PC is that it is "battery operated" driven by an internally mounted battery. This feature is provided because the computer can thus be used in a mobile environment where commercial power source is not usually available. A battery used by a notebook PC is, in general, formed as a "battery pack," consisting of a plurality of rechargeable battery cells, such as Li-Ion, NiCd or NiMH battery cells. Although the battery pack is rechargeable, to recharge it 2 to 3 hours is required, whereas its operating capacity following each recharge is at most 2 to 3 hours. The long period of time required for charging is a fatal problem as far as the use of a battery-operated machine is concerned, and this is why a user is required to carry at least one extra battery pack. Therefore, in order to extend the operating period for batteries, various power saving technologies have been proposed for notebook PCS. The power saving function is another feature of notebook PCS.
Recently, because of ecological considerations, there has also arisen a demand for the incorporation of power saving features into desktop PCS that are usually installed in offices and are driven by seemingly endless, commercial power source. The Environmental Protection Agency (EPA) announced a self control program, called "Energy Star Computer Program," in June, 1993, requesting that the power consumed by a computer during a standby state shall be set to a predetermined standard level or less (a driving power of 30 w or less, or 30% or less when a CPU is in full operation mode). Computer makers, therefore, have competitively developed and manufactured products that satisfy the proposed standards.
The basic idea on which power saving designs for various electric/electronic apparatuses are based is the halting of the power supply to unused devices or circuits. In U.S. Pat. No. 4,933,785, for example, disclosed is a technology whereby the power supply to internal electric circuits within a hard disk drive (HDD) is halted step by step in accordance with its operational condition (i.e., the elapsed time since the last disk access) (see claim 45 in this publication).
On the other hand, expansion of multi-media functions has been rapidly advanced for the latest PC models. That is, functions by which not only computer data but also various data elements, such as motion pictures, still pictures, voice and character data, are decoded and processed in a computer system. Since so-called multi-media data are stored in huge files, such as files for color images, a multi-media PC is required to mount an external storage device, such as a CD-ROM drive or a DVD (Digital Video Disk or a Digital Versatile Disc), that can process an exchangeable storage medium storing a great quantity of data. Further, since the application of the multi-media function is being expanded to encompass the communication/broadcasting fields, such as for video conferences or for color facsimile communication, a device such as a modem or a LAN card should be installed in a computer for connection with a network. In addition, ZV (Zoom Video) standards that are compatible with a PC card slot have also appeared. A ZV port compatible PC card provides a fast motion picture display by transferring data directly to a video controller.
The sound function as well as the video function is indispensable to a multi-media PC because many of the peripheral devices associated with the multi-media function handle audio data as one type of multi-media data. The sound function of a PC is implemented in such a manner that an audio controller on a motherboard provides mixing/volume control and performs the D/A (digital/analog) conversion of audio signals that are output by individual peripheral devices, and that an audio amplifier amplifies the resultant signals and outputs the amplified signals through a loudspeaker (or outputs them across a line to an external audio device).
Let us return to the power saving design for the PCS. As previously described, the basic power saving design is the halting of the power supply to unused circuit modules. However, little consideration has been given to providing a power saving design for the sound function of the PC. This is because it is difficult to precisely detect an unused state (i.e., an audio signal muted state) for the sound function since there are many peripheral devices, such as a CD-ROM drive, a modem and a beep sound generator, that output audio signals.
Most of the audio controller chips mounted on the motherboard of a computer have a power saving function that can be set or canceled by software. In other words, a specific bit of an I/O register of an audio controller is defined as a "power control bit," and when certain software (e.g., a device driver for driving the audio controller) writes a flag "1" to the control bit, the system can fall into the low-power consumption state in which the operation of the audio controller is disabled.
However, if the sound function of the system (e.g., an audio CODEC chip or an audio amplifier) is mistakenly disabled while the CD-ROM drive is playing audio (CD-DA) data, the audio data retrieved from the disk can not be output. This occurs because even when the drive is returned from the muted state to the unmuted state, the computer may not recognize such a state transition and thus will not enable the sound function regardless of the activation of the drive. An external storage device, such as a CD-ROM drive, that also serves an audio function can play audio data not only upon a host command from the computer but also upon the depression of a play button provided on the drive unit. When the play button is depressed, it is impossible for the computer software to detect the mute/unmute state of the drive. If the normal operation of the sound function is expected, the sound function must be maintained active constantly. That is, the use of the power saving function of the audio controller is substantially impossible. For example, the audio amplifier in the active state constantly consumes several hundreds miliwatts of power, which for a battery-operated PC is too much to be ignored.
On the other hand, the muted state is defined for various audio products, including CD players. However, in their original forms audio processors are not external devices intended for connection to a computer system. That is, an audio product is a stand-alone machine that is not under the control of the computer system, and does not have a mechanism that can inform an external computer system of the muted state of the machine (i.e., an audio product is not connected to the computer system through an interface).
CD-ROM drives having an audio function have become popular. In Japanese Unexamined Patent Publication No. Hei 8-36829, for example, disclosed is a replaying apparatus for a CD (Compact Disk)--DA (Digital Audio) disk, which includes a mute circuit, and a video CD disk. However, the replaying apparatus merely incorporates a mute circuit that prevents the occurrence of unwanted and uncomfortable noise when a CD-ROM is mistakenly loaded and sound is replayed, and does not have a mechanism for notifying an external apparatus of the internal muted state. The replaying apparatus is a stand-along machine, and in its original state has no interface for a connection with an external computer system.
In Japanese Unexamined Patent Publication No. Hei 7-312014 is disclosed a CD audio/ROM player. The player has a host computer interface for the reading of computer data from a CD-ROM disk to an external computer system, or for the receipt of operating commands from the host computer. However, the mute function of the player merely prevents the release of noise though a loudspeaker connected to an audio terminal while the computer data are being retrieved, and a microcomputer processing retrieved data supplies a mute signal only to an internal audio circuit (for an example, see [0015] in the publication). In other words, a mute signal output by the microcomputer is used only inside the player, and is not output to the external apparatus. Accordingly, it is impossible for the external computer system on which the player is installed to identify the muted state of the player and perform a power saving operation.
If peripheral devices having an audio function notify the computer (i.e., a host) of their muted states, the host can precisely understand the period that the operation of the sound function is not necessary, and can save power on the sound function. However, as is described above, a CD-ROM drive, which is one of the multi-media devices, does not output externally a mute signal.
The audio signal input terminal of the computer is connected directly to the sound function, regardless of whether the peripheral devices are in the muted state. Therefore, an unwanted current flows along the audio signal line during the operation of the drive, which results in the deterioration of the S/N ratio.